Annabel Smyth:
what I have always wondered is how does New York manage to run a
24-hour service, or is this because they can often re-route trains
if they want to close a section of line ...

Dave Arquati:
Because some New York lines have four tracks (for fast/slow trains) of
which one pair can be used for all services at night.

Robin Mayes:
You'll find only the 4 track lines continue to run 7 days a week,
24 hours a day. The lines with only 2 tracks are shut at times for
engineering works and bus replacement services are offered.

True. However, almost all lines do run 24/7 *except* when this sort
of closure is needed. London's tube tunnels aren't big enough for
people working there to step aside and allow a train to pass, making
various kinds of work impossible that in New York would take place
during operating hours. (However, here in Toronto the tunnels *are*
big enough, and the TTC says they still need all the overnight shutdown
time that they now have, so maybe that's not much of a factor.)

I also recall one visit to New York on a Sunday afternoon when I was
riding on a 2-track line and saw a sizeable chunk of wood, painted
yellow and striped with black electrical tape, handed to the driver --
sure enough, it was a single-line token, and the other track was closed
while work was going on on it.
--
Mark Brader, Toronto | "I don't have a life; I have a program." --the Doctor
| (Michael Piller, Star Trek: Voyager, "Tattoo")

My text in this article is in the public domain.